238 



THE AGRICULTURAL NEWS. 



July 23, 1910 







1S2. 



FUNGUS NOTES. 



OAOAO SPRAYING IN TRINIDAD. 



In the article on Cacao Canker which appeared in the 

 last number of the Aijricidtural News, reference was made to 

 the results of experiments on cacao spraying, obtained 

 b}- J. B. Rorer, M.A , Mycologist to the Board of Agriculture 

 in Trinidad. As these results may be of some interest to 

 readers, it is proposed to give a more detailed account of them 

 in this article, and to mention, in addition, a few other con- 

 siderations which have to be taken into account when proposing 

 to extend the treatment to some of the other islands of the 

 West Indies. A full account of these experiments, written 

 by Rorer, will be found in The Bulletin of tlie Department of 

 Agriciiltufe, Trinidad, Vol. IX, p. 10, and the Annual Report 

 of the Mycologist to the Board of Agriculture, Trinidad, 1910. 



Preliminary experiments were conducted in -July, 1909, 

 at Santa Cruz and Tunipuna to determine the effect of various 

 strengths of different spraying mixtures on Hower buds, 

 flower.s, young fruits and leaves. The sprays u.sed were 

 Bordeaux mixture of two strengths, the first containing 

 5 Bb. of copper sulphate and 5 D). of lime to .50 gallons 

 of water, and the second containing 4 lb. of copper 

 sulphate, and 4 lb. of lime to the same volume of water; 

 in addition, various strengths of a proprietary lime-sulphur 

 solution were also experimented with. Both strengths of 

 Bordeaux mixture were found to injure the flower buds, 

 flowers and tender leaves, but were harmless in the case 

 of .small fruits and older leaves. The same was true of 

 the lime-sulphur wash when diluted down to 1 part in 

 25 of water; but when diluted to 1 in 30, it was harmless 

 to the flower buds and the few flowers that were open at the 

 time. The injurious effect of the Bordeaux mixture was 

 probably due, to some extent, to the wet weather. 



Following on these preliminary experiments, work on 

 a .somewhat larger scale was undertaken, for which a block 

 of 1,000 trees was selected, and divided into two equal parts. 

 All the trees w ere of the same age, and the general conditions 

 of soil, drainage and shade were identical, and, moreover, the 

 results of a picking made before the spraying was commenced 

 indicated tliat the yield of cacao from each plot was practi- 

 cally the same, and that the relative proportion of black cacao 

 was identical for each plot. The term 'black cacao', used 

 throughout the experiments, is intended to indicate pods 

 which have been so attacked that the beans have been 

 infected. Xo attempt was made to differentiate between the 

 various diseases which were responsible for the black cacao. 



Plot 1 was sprayed on September 6 and 2 1 with Bordeaux 

 mixture 5 5-.50 (as indicated above), while plot 2 was left 

 un.sprayed, as a control. The spraying was done with a barrel 

 pump, fitted with two 7.5-foot leads of hose, and bamboo 

 exten.sion rods 8 feet in length, with double Vermorel nozzles. 

 The object was to spray each tree thoroughly, including the 

 leave.s, pods, trunk and branches. .\t the time of .spraying, 

 the trees were covered with young fruits from A-inch to 

 3 inches in length, and bore a few older pods. "A small 

 picking was made in September, when the yield from each 

 plot was found to be the same, as the ettect of the spraying 



had not yet shown itself. Two main pickings were made, on 

 November 12 and December 11, when the following results 

 were obtained: Plot 1 gave a total of 3,219 pods, of which 

 2,930 were sound and 289 were black, so that the percentage 

 of black pods was 8'9. The control plot No. 2 gave a total 

 of 3,104 pods, of which 2,182 were sound and 922 were black, 

 i.e., 29 ■" per cent, of the pods were diseased. An examina- 

 tion of these figures shows that not only was the percentage 

 of black pods greatly reduced, but at the same time there 

 was an increase in the total number of pods obtained 

 from plot 1, as compared with those obtained from plot 

 2. As a result of these two factors, the sprayed trees 

 from plot 1 yielded 189 lb. more good cacao than the 

 unsprayed trees on the control plot. Two other pickings 

 were .subsequently made on January 14 and February 15. On 

 this occasion, plctt 1 gave 2,829 pods of which 2,677 were 

 sound and 152 or 5'4 per cent, v/ere black. Plot 2 yielded 

 1,629 pods of which 1,308 were sound and 321 or 19"7 per 

 cent, were black. The sprayed trees yielded 1,200 more pods 

 than the control plot, probably because several pods were 

 saved from fungus attack, when quite small, by the spraying 

 which had been carried out when the)' were very young. As 

 a result of the four pickings, 1,315 more pods were obtained 

 from plot 1 than from plot 2; 7'3 per cent, of the total 

 number from the sprayed trees, and 26'3 per cent, from the 

 control plot, were black. Owing to these two factors, 2,117 

 more sound pods were picked from plot 1 than from plot 2. 



In addition to giving the great increase in yield indicated 

 by these figures, spraying is beneficial to the trees in other 

 ways. As was indicated in the article in the last number of 

 the Ai/i-iriiltiiiYil A'ews, Rorer has found that canker in Trini- 

 dad is due to the fungu.s, P/ii/toj>/ithora omnivora, which causes 

 black rot of the pods, and the reduction of the number of 

 diseased pods due to the spraying, together with the 

 direct effect of the spraying on the trunks of the trees, would 

 probably tend to greatly reduce the amount of canker 

 on any given plantation. This is a factor of considerable 

 importance. In addition to this, the spraying reduces several 

 minor diseases, such as thread blights, anthracnose of the 

 pods, etc, and keeps the tree free from moss. It would prob- 

 ably also have a considerable eft'ect on the presence of brown 

 rot, die back and stem disease, due to Lauodiplodia theobro- 

 mae Another factor that must be taken into consideration is 

 the cumulative effect of the spraying, as a result of which the 

 increase in yield would be progressively greater for several 

 years until a point was reached at which the trees were giving 

 their maximum yield under the general conditions which 

 obtained on the plantation. 



\Miile calling attention to the interesting results gained 

 by Rorer, it i.4.not the purpose of this article to unduly 

 emphasize the importance of spraying in connexion with cacao 

 cultivation. In the case of man)- of the islands of the L&sser 

 Antilles the general conditions of cultivation, the lie of the 

 land, and the difficulty of obtaining water, often render the 

 adoption of this practice almost an impossibility. It should 

 be remembered also that to obtain the best results, spraying 

 should not be employed alone, but in conjunction with general 

 sanitation of cacao plantations; such measures are the 

 careful burial with lime of the pods, and of all diseased 

 material, whether pods or twigs, removed when pruning, 

 together witli careful tarring of the wounds thus made. 

 Under the conditions in which all these methods can be 

 reasonably employed, it would probably be found that a very 

 large increase in yield would be obtained which would not 

 only cover the expense involved in carrying out the remedial 

 measures, but also ensure a very considerable increase in 

 profit. 



